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Jens

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  1. Thanks for the more detailed info about the detection possibilities! If you look at it from a less theoretical but a bit more practical level (even though it is still theory of course ): The issue is the energy. Traveling is highly energy expensive. It is difficult to overcome physical borders. (For example the fastest non-military aircrafts we as humans are using today are slower than those 20 years ago and thirty years in the past people predicted that we will fly to the moon for holiday trips by now.) Let's stay within known physics. Let's assume there is no miracle way of converting arbitrary mass fully into energy. So the most powerful energy resources for intelligent species are radition from the various suns (especially if you come close) and nuclear fusion. But taking atoms ("minerals") from somewhere outside the planet you are living is extremely energy consuming and time consuming - especially if you have to leave your solar system. It will never pay off -- especially if you count on clever ways to obtain what you need via chemical material improvements instead of beeing dependend on scare atoms. (and remember that hydrogen needed for nuclear fusion is not scare anyhow.) So any civilization would rather use something else than steel instead of carrying iron from another solar system. Or use more clever doted mixtures instead of beeing dependend on rare earth atoms. Note that I use the term atoms, since obtaining more atoms is the only thing you cannot do with chemistry. Nobody is interested in specific minerals, since you can all build them via chemical means with millions of times less energy than you need for interstellar travel. So I think viable reasons to travel to the next solar system are to live on another planet or to do research but not for atoms (and definitely not for minerals).
  2. To discuss the possibilities of life, it makes sense to consider the 3 main restrictions for life on a planet with water: A: the carbon available to life B: the energy available to life C: the chemicals which can be used as electron source (to reduce CO2) This is roughly the situation on Earth (assuming the standard way of thinking that life started after time point 2. I doubt this -- see initial post of this topic.) A1: High levels CO2 and initial load carbon containing molecules of all kinds are available (e.g. all kinds of condensed forms of CH2O like sugars) A2: no changes A3: Life has transformed the initial load carbon into biomass and some into CO2 or CH4, but there is still a huge amount of CO2 available for life. A4: Life can use carbon more efficiently by obtaining energy from light. A bit more CO2 is transformed into biomass. A5: Photosynthesis dramatically reduced the amount of CO2 available. Today in some tropical regions CO2 is already the limiting factor for some plants. However, for other regions and C4-plants light energy is still limiting and not CO2. So overall energy is still the limiting factor. B1: Energy is available as condensed phosphates (pyrophosphates) and other condensed molecules of all kinds that provide energy simply by hydrolysis. Those condensed molecules are formed in cooking and drying on hot rocks (no burning since there is no O2) and are than transported by liquid water to other places as soon as the rock is covered with water again. In addition to the condensed molecules there is also chemicals produced as from volcanoes today: e.g. H2 and H2S which can produce energy during chemical reactions with other inorganic compounds. B2: The condensed molecules have undergone (very slowly) spontaneous hydrolysis, so that much less is left. B3: Life consumed all the remaining condensed molecules, so chemical energy becomes the limiting factor. B4: Using light as energy source provides a dramatic extension of the potentially available energy for life. C1: The initial load of carbon has all kinds of different oxidation states, so electrons can be re-arranged to produce biomass out of it (and CO2 or CH4 as end products). In addition there are reduced inorganic molecule species (like H2S which can be used to reduce CO2. Those are provided constantly by volcanoes and have accumulated in the oceans. C2: no changes (at least following standard assumptions that life emerged late) C3: Only the inorganic molecules are left. The rest has been transformed into biomass. However, life needs more energy than reducing power, so the energy is the limiting factor. C4: Using light energy but other molecules than water as electron source, makes the reduced molecules the limiting factor for still growing the biomass. And in addition some reduced molecules can be used which could not be used without light energy. But still life is dependent on volcanic activity. C5: The final (and most complex) way of using light energy is the current photosynthesis in which the energy of multiple photons is added up to ultimately take electrons from water (which is available in ‘unlimited’ amounts) and produce O2. So the electron source does not limit life any longer. I will (in ~10 days) make a corresponding picture with an explanation for the case of Jupiters moon Europa (under the theoretical assumption that life emerged there, too) -- and discuss the situation.
  3. Yes, I care about common life! Actually for me life (in any form) is just incredible. ... and if it is only like bacteria, which are already very complex. There is nothing like primitive life left, especially if you look at the metabolism. Every microorganism left today which is capabable to survive wihtout eating other life forms or living from their remains, is even more complex in metabolism than animals. Of course animals have a much more elaborated regulation and structural features than bacteria. The basic machinery of life on Earth is the same for all life forms. I gave reasons that any life is very rare (see the first original post). I restricted the statement to our galaxy only for the reason to not have a dicussion about the infinite univers (which would be another topic). See my post on April 1st in this topic. On Earth life is now independent of scare reduced molecules from volcanism (thanks to photosysnthesis). However, it still needs CO2 as a carbon source, which is constantly refilled in huge amounts by volcanos. If this would not happen, the carbon lost in the sediments would constantly decrease the amount of carbon available for life. So even though life is recycling carbon it would become less and less over time. (On Europa this is a bit less of an issue, since the giant ocean is probably full with huge amounts of CO2.) Without photosynthesis the critical thing for life is reduced substances (Xred) which can be used to take electrons to transfer them to CO2 to make molecules of life out of CO2. H2O2 can not act as such a substance. The area (as distance form the center of gravity -- the sun or a big planet like Jupiter) where a planet or moon collects much H2O is always also the area where oxygen (as atom in any form) is quite abundant. The whole surface of Earth is full with fully oxidized chemicals -- like stones and water) On Earth you had and still have multiple sources of Xred: The initial load of carbon species coming from somewhere else (via meteorites.) H2, H2S, S8, COcoming from volcanos (I have to look for other reduced molecule species, but these are the main ones). thanks to the energy of light life can also make the chemical impossible: to take electrons from abundant H2O and make itself independent from the rare other sources of Xred. This is called photosynthesis. However, photosynthesis is a rather complex thing, especially the final one taking the electrons from water. Life on Earth and nowhere else will start with photosynthesis. maybe cracking of CO2 or carbonates (the correspnsing salts) at very high temperature on the surface of molten rock. This might produce oxygen species and more reduced forms of carbon. I have to check this one out. On Europa things look different: Source 1 of course will not last forever (especially if it is shielded via the ice). As soon as life has oxidized it all (with the help of the H2O2 from the surface) it is finished with life. Source 3 will not work, as I have pointed out above (in an earlier post at April 1st). Volcanism is the only source (both behind source 2 and source 4) that I can see working at Europa. (At least from what I see by now).
  4. Yes, I fully agree. Of course I am not doubting evolution as a slow gradually process. And of course what is shown in some "science" fiction cinema films where you can watch evolution happening within some minutes (mainly as otherwise the film would be very boring and the film makers need to earn money) is complete nonsense (and you are right, if you argue against this). What I mean is a scientific concept. I will try to find different words: Evolution is mutation and selection. Even though the mutations happen random and typically at roughly the same pace (since the reason for them is chemical statistical behaviour or radiation which is roughly constant), the selection part is of course heavy dependent on competition. And competition is not constant at all. So overall evolution over one long time period (let's say 100000 years) can be of much different speed than for another time period which is exactly as long. More concrete: If there is an opportunity for life or a life form (no matter if it is microbes or big animal life forms) to colonize an inviting habitat empty of competitors, there is for a longer time period no competition. So for many generations a given individual do not need to be really fit to have multiple descendants. This means for many generations a mutation which is not lethal but disadvantageous is not removed from the gene pool and many individuals are carrying it. Now imagine there is a certain feature (like photosynthesis using H2O instead of H2S as input) for which you need multiple proteins (lets say 5) to change simultaneously to function but all the changes alone are disadvantageous. Only in combination they provide a benefit. If there is stiff competition this will never happen, because the individuals with one or multiple of these mutations will die. So there is never an individual that has the chance to accumulate all five mutations. However, this looks completely different, if there is no or only little competition. This is why from an archaeological view there are some time periods in which evolution made big "jumps" forward and others in which evolution was much slower. Note that "jump" here still means many ten-thousand years. Those time periods on a regular basis go in line with colonization of an habitat without much competition. Or in genetics terms: The molecular clock of mutations is constant. The molecular clock of evolution (mutations forward, selection, mutation backwards, selection, ...) is not constant, since selection pressure is not constant.
  5. O.k. You are right. That analogy was too simplistic. I will try to think of a better analogy. Mainly because of mineral catalysis you cannot compare it. Chemical systems can much easier produce positive feedback cycles (however, that is not enough for evolution to start). But there is also near random chemistry at high temperature condensation and to chain up macromelecules initially. Nevertheless, you are right. Maybe I better try to list what is all needed for evolution to start. Back to potential life on Jupiter moon Europa There are two main scenarios for the biochemistry on Europa: A) The mantle of Europa is solid and there is no volcanism any more. This is because Europa is much smaller than Earth and volcanism should have stopped already long time ago. B) The mantle of Europa is liquid and there is volcanism left. This is because the tidal forces of Jupiter keep the mantle liquid despite its small size. In this post I will focus on scenario A: Since photosynthesis does not seem to be plausible (see my last post about Europa in this topic), the main issue in this scenario is to find a substance which can be oxidized to balance out the reduction of CO2. Water (H2O) on the surface of Europa which is under heavy bombardment of radiation can only be transformed into H2O2, O2, O3, H2 and into the radicals OH, O2-, and H. H2 and H are quickly lost in space due to the low gravity of Europa. The remaining molecules and radicals are all highly oxidizing. In principle H2O2 could also serve as reducing agent and be oxidized to O2 but the reaction does not work in the wanted direction but the other way round: 2 H2O2 + CO2 <-- 2 O2 + H2CO + H2O (H2CO as example for a reduced biomolecule) The brown color on Europas surface around the cracks looks like Fe(OH)3 - rust. This also means fully oxidized, but of course it can also be a crude mixture of anything. Even if you assume that a lot of reduced carbon species (like H2CO) were coming initially from meteorites this means in this scenario that life could gain energy by oxidizing them to CO2. Oxidizing will happen with the help from the oxidizing substances coming into the ocean from the recycled surface (O2, H2O2). Part of the reduced carbon species are used to build the organisms. This means the basis for life will continuously smaller and smaller. In such a scenario very likely there will be no life left any more, as soon as all the reduced carbon species have been transformed into CO2. So scenario A probably means there is no life left on Europa. (Of course only if there was any at all – which I doubt – see the initial post of this topic.) Does anybody knows if the magnetic field of Jupiter bring in many free electrons from space to Europa? This could be the source of substance which can be oxidized. The free electrons can reduce Fe+III to Fe+II or reduce sulfur in sulfate. Reduced sulfur or reduced iron would solve the problem.
  6. Yes. But I also agree to Moontanman. In any case, it is not really important. On early Earth (or any other planet which will end up with oceans of liquid water) you have plenty of chemical energy on the hot mineral surface and evaporating water locally provides all you need to create energy rich condensed molecules out of things like H2CO initially from asteroids (or even CO from Earth itself). I guess this will be quantitatively much more relevant than lightning. I think we know a bit more in microbiology now. Abiogenesis is a complex multi-step process and will not just happen at once by a lightning into a pond. (of course - as you know - ribosoms will not be created at once by pure chance). The present life makes it impossible for this complex multi-step process to happen again in nature. And of course I agree to the "and oh what a big if". If anybody could repeat abiogenesis my complete thesis (see first post of this topic) is wrong. Thanks for the interesting Darwin quote. (Off topic: I always appreciated your clever posts. I am currently ordering one of your book recommendations. ). Interesting. Even though this goes into the direction of my thesis, I still have some concerns: How sensitive are our detectors? Would we really be able to to detect them? If the minerals are somehow the same in any habitable solar system, why should you (as an extraterrestrial) pick them up from another solar system instead of the one you are living in? I recommend to have a look into a biochemistry book. Even if you take of everything optional from the simplest current life forms they are incredibly complex. Actually from a biochemistry point of view a human is in the same order of complexity than a "primitive" bacterion (actually there is no primitive life). Abiogenesis is the process of how to transform chemicals into a system which can evolve. After evolution has started everything is reasonable plausible. Currently we cannot explain abiogenesis (yet), even though a lot of progress has been made. To make a comparison: Let's pack a 100 billion of planet surfaces (to equal the bigger size of microrobots compared to chemicals) with metal pieces of all kinds, shake the whole thing add some random current and hope that a self-replicating robot comes out. You might tell me that's impossible. I agree. But this is how I feel about abiogenesis (since I am an expert in biochemistry). Of course I do not claim that there is some intelligent design (and this is not the topic here to discuss it!), I just want to say, we are still missing something. And abiogenesis looks really like an improbable event.
  7. This will be a longer post, but I think it is needed . Richard Greenberg – like many others in astronomy – is setting a strange (from a scientific point of view) focus on animal-like life forms. This has become very common in astronomy missions, because of 3 reasons: 1) It is fascinating. 2) It is needed to get the big public money for those missions. 3) Ignoring microbiology. I agree with the first 2 points. So I will try to give more insight on the third point: Life is a chemical thing. There is no way to discuss abiogenesis without discussing chemistry. Here I consider only life forms based on carbon chemistry in a water environment. (There are good reasons to assume that this is the only way of life). No matter, at Europa there is plenty of water and there is carbon. To exist all life forms need an energy source, a carbon source and another substance to balance out the redox reactions done with the carbon source to transform the carbon source into bio-molecules as part of the life form. There are two main ways of obtaining the energy and the carbon: Either the life form is taking both from the inorganic environment (autotroph life forms) or from other life forms (heterotroph life forms), no matter if those other life forms are still living or dead (means you just take the molecules of them after they died). Of course heterotroph life forms cannot exist without autotroph life forms. For example: Every single bit of energy your brain or your muscles are consuming (or wasting) had initially been collected as sun light by cyanobacteria or their degenerated form – the chloroplasts in plants, no matter if you eat animals or plants. Of course heterotrophy life forms always form a smaller part of the overall life. And of course in the beginning the first life forms could only be autotroph or use organic material which was in the environment by chemical processes and not by biological processes. So even if live started by using organic substances out of the environment it will quickly use all them up and should become autotroph as soon as possible. So instead of speculating on crazy shapes and forms of giant animal-like and plant-like life forms real understanding comes from investigating the basis: The microbial autotrophic life. In a simplified representation this means the chemical basis is the following (of course other atoms like N, P, S are also needed): Autotrophic life: CO2 + H2O + Xred + Energy --> Biomolecules + Xox Heterotrophic life: Biomolecules + Yox --> CO2 + H2O + Energy + Yred X and Y can be any substance that can undergo a redox reaction. X and Y can be the same or differ. The energy in autotrophic life might simply come from the reaction of Xred to Xox or might come from another independent chemical reaction. In plants on Earth Xred is H2O and Xox is O2 and energy comes from sunlight, in animals on Earth Yox is O2 and Yred is H2O. Applying this to Europa: What is the carbon source on Europa? CO2 had been detected. So it seems it is like on Earth the carbon source. If there is still under-sea volcanism on Europa there is a constant input on new CO2. Even though Europa is smaller than the Earth the tidal effects of Jupiter might had kept the inner core still as liquid magma. If this is not the case, there is most likely a huge (but fixed) amount of CO2 in the giant ocean (150 km thickness). This carbon then has to be recycled between life forms competing for it. How to do the redox reactions and how to get the energy? If CO2 is the carbon source (like on Earth), life forms need to reduce it. Molecular oxygen (O2) is not helping here, since it oxidizes other chemical substances and cannot at all reduce substances (it cannot act as Xred). So the main question is how to reduce CO2 and not if O2 is present or not. Without any autotrophic life forms there will be no animals that could consume the O2 to do the reverse reaction of the autotrophic life forms. Sulfuric acid and the corresponding salts are present on Europa but this does not help, since they are also completely oxidized already and cannot reduce CO2. One source for reducing power is - like on Earth - photosynthesis. With the help of light power (otherwise it would be chemically impossible) the reducing electrons are torn out of water molecules (which are always easily available). A certain part from the light power can be used (like on Earth) to create chemical gradients as internal energy form to drive life. However, Europa is different from Earth: - The distance from the Sun is 5 times bigger – means 25 times less sunlight then on Earth. - Only few cracks (or none) are active at given point in time. Active means they are opening and closing in a daily cycle. So there is not much surface which receives light. (Note that organisms trapped in permanently frozen ice below the surface might receive sunlight, but will not have steady access to CO2 and other substances (like phosphate or nitrogen salts) to grow in frozen ice. - Like mentioned by Greenberg the uppermost thin layer of the water and ice is killing life, since Europa has nearly no protecting atmosphere and Jupiter is causing a lot of molecule breaking radiation to come in. - Crushing in the daily closing cracks will anyhow kill all plant-like organisms. - Greenberg is assuming a 1000:1 ratio depth of the crack versus width. So even assuming a 200:1 (if the cracks are more distant than 100 km), this means the liquid water is very much in the shadow, since it does not reach the top (water is heavier than ice). - If data is correct, it took about 1000 million of years of evolution on sunny Earth before emergence of photosynthesis with H2O as Xred, and probably half that time with other substances (H2S) as Xred. If Europa was covered with ice for most of its existence, photosynthesis probably never have evolved on Europa. - The biggest issue is that those organisms that are enough at the top of the 1-10 km deep crack to receive light will all be squeezed out on the surface (and not down to the ocean) at a daily basis (a day at Europe takes 85 hours). The biomass lost by this cannot be replaced quick enough with growth under so little light and so low temperatures. So it does not seem to work out for photosynthetic autotrophic life forms on Europa. Of Course, you can assume, that the life forms live for a short cycle of let’s say 100 days (since they repeatedly have fallen back into the crack after being squeezed out once a day) until they finally left at the outside. Then they have to wait about 1 million years until this piece of the surface has been recycled into the ocean. Of course this scenario also means that the top of the crack after the first day is filled with crushed ice and not with liquid water. I guess this does not seem very plausible. But still there are possibilities for life on Europa. There are other possibilities for getting energy and for Xred on Europa. I will come to this next week.
  8. I have read the book "Unmasking Europa" from Richard Greenberg now. (off topic: From my point of view it is a great book! The author has suffered from a scientific community that is very resistent to new views for many years, so that the scientific predecessor of this book and this book was is main way to get the story out. So he is directly attacking people. This makes the book a very good reading for everybody who has to make his/her decision to stay in research or better make a life outside the scientific community. Depending on your personal taste you might also find this disturbing. Of course he has a certain self confidence (as otherwise he would not have written the book) but in contrast to many other proffessors he is not only mentioning his group as a whole -- and thereby only himself -- but the different contributions of his students by name.) From my point of view he clearly prooves that Europa has a relativly thin ice layer (1 km - 10 km), which is cracking on a regular basis so that the liquid water below is directly connected to the surface from time to time. Of course this makes Europa a much more probable place for life than if the ice layer was 20 km - 50 km thick and never opens up. And to my point of view he is right in his proposals to plan for example a mission to investigate the ridges instead of mission impossible to drill through kilometers of ice. (I will provide detailed comments on the chapter 17 "The Biosphere" tomorrow, this is more my terrain.)
  9. I got the book "Unmasking Europa" a few days ago and read through the first 62 pages (out of 270). It is worth reading. (off topic: Also the part showing from the authors point of view (Richard Greenberg) how big research projects are biased by humans which have to make their living and career in science. Of course I cannot judge, if he is right in some accusations, but what is described as humans frictions seems likely to be true, since this is just what you always see in huge organizations, no matter if it is business or science. ...and the author also states that the convervatism he is criticizing is definitely needed in some parts of big space projects -- so he tries to understand the other side.) I share the authors (Richard Greenberg) wish to improve science independent on any personal interests (like research funding). Since I do earn my money in a field completely outside science and do this as hobby only I do not have to defend my position just to obtain more papers. --> I have not reached yet the pages relevant to the critical biological part. I will do so over Easter holidays. (sorry for being slow, but I only have a few hours for this per week left between work and family ) my text Yes. I agree. What I meant goes one step further: Sometimes for making bigger evolutionary steps forward multiple mutations (let's say 3) which have a real effect on the organism (and are not neutral with regards to phenotype) are actually needed at the same time. Since of course it is very unlikely that they all 3 happen the same time they happen sequentially and the intermediate organisms with only 1 or 2 of them need to survive. Evolution is typically rather quick if those intermediate steps are neutral (or even advantagous). However, if those intermediate steps are clearly not positive, the orgnisms will not survive enough generations to have a chance to make the last mutation needed, if there is strong competition. Strong competition you have if the organisms have already adapted quite well to a stable environment. This means evolution will be trapped in a local minimum and will not make bigger steps any more. This is the reason why typically the largest steps in evolution always happen, if organism can colonize a biotop without competition. Example: There seem to be evolution paths in which each small step form a slight advantage, so that you quickly obtain the same results: Transforming an air breathing terrestrial animal (a carnivor dinosaur or mamal) into nealry the same shape marine fish hunting animal like ichtyosaur and dolphine actually happend twice in evolution. Even though mamals had been there all the time of the dinosaurs, they never made it to dolphins as long as the dinosaurs where there. So of course competition often stops evolution from going certain paths. In this example the path from a air breathing animal to a quick air breathing marine fish-like looking animmal seems to be much simpler than the path from a fish taking oxygen out of water to to a fish taking oxaygen out of air. The fish-hunting fish are trapped in a local evolution optimum and they cannot go out of it, no matter if much more time is given. Before the time of the dinosaurs there had been dolphin-sized (and larger) fish-hunting fish in addition to the sharks. Marine dinosaurs and later the marine mamals have taken their places.
  10. I have read through the comments in your link: It is a kind of scientific hoax: http://www.slate.com/blogs/bad_astronomy/2013/03/11/meteorite_life_claims_of_fossils_in_a_meteorite_are_still_wrong.html So it is good to get some attention. But no science. No extraterrestrial life yet. And yes: the quotes above where quotes from the web page itself and not from Gaylord. (I thought this was clear, sorry if that has caused confusion) Thanks for providing the link Gaylord!
  11. If this is true, I am wrong. I will try to get the article. (Even though I am reading a lot of scientific books and original publications, I am not working as scientist anymore and have no free access -- but maybe google scholar helps) However, first impression is not too good: I add: Diatoms are very complex protists (Eukarya). They appeared on Earth only about 200 million years ago. Like plants they have chloroplasts (which were initially coming from endiosymbiosis of cyanobacteria). As protists they are roughly a factor of 100 bigger in volume than bacteria or archaea. Such organisms have not been the source of of life (via panspermia) on Earth. They just have very hard cell walls containing silica (so this inorganic substance can also be made by living beeings).
  12. Thanks, I will buy the book ("Unmasking Europa: The Search for Life on Jupiter's Ocean Moon") and read it and post the comments here. (Will take about 2-3 weeks). I feel the same. (Off topic: Unfortunately in Western Europe you nearly never see the Galaxy and only a few stars. Hope that people think about it nevertheless...) It is impossible to apply any mathematical model, if we do not know how abiogenesis happened (or are even able to reproduce something like it in a laboratory). So I do not follow this statement, but actually that does not really matter (it is anyhow too far off). I intentionally have taken "Galaxy" and not "Universe" to exactly not have a discussion how big our universe actually is (which is a separate topic). So you are right in pointing this out. looking forward to read your opinion
  13. Thank you for the interesting link! Directly on this page Jack Lissauer is quoted: This is exactly what I mean. And I push it even more: Those climate changes actually speed up evolution. If you do not change the environment evolution is not very quick because it gets trapped in local optima quite quickly. Another obervation: On the page they state: I always thought that Mars has lost its water because it is smaller --> got solid internally --> no magnetic field --> no protection from sun wind --> ionisation of gas (e.g. water) --> loss of the atoms or H2 formed, since gravity of Mars is not enough. May it be that even the Science web page is trying to make interesting news ? (this is a business after all) Interesting. Do you have any idea how I can obtain more details since it is only stated "Using estimates for the production of oxidizers at the surface". I wonder what he actually means, since O2 does not form easily (since it is highly reactive). At a first glance this looks like inventing an interesting story (Since many non-biologist considers only animals and plants as life and are not interested in life you cannot see -- and some even think only of animals if the use the word life ). However, with more details I might change my mind completely. I am not convinced at all, because I cannot imagine that a several hundred meters thick ice layer even if moved continously can move more oxygen (O2) into the water than on Earth with liquid water moved by the wind and an atmosphere with 20% of O2. (so not explaining the details is highly suspicous) Of course -- if there is life -- all the O2 in the water will be consumed (like on Earth) mainly by microorganisms. Microorganisms are doing the same thing as animals: They take energy rich molecules for mother life forms and let them react with O2 to gain energy. They will not let the slightest chance for bigger fauna to consume O2. On Earth this is only working, because there are giant amounts of cyanobacteria (directly or as part of algae) in the oceans that produce O2 all the time (and the vast majority -- in quantative sense -- of other life forms are just using directly or indirectly the molecules produced by the cyanobacteria). This is not possible on Europa, because the oceans are completely dark. In addition the wording looks like the authors have not included (intentionally?) the invisible and small animals (microfauna) that the macrofauna actually eats and that consume of course in total much more O2 than the macrofauna. So this also looks like story-inventing. Just in case: Do you know any free articles behind? (probably I have to buy the book mentioned. So story telling worked )
  14. The tite of this topic seems to be confusing. Within the next two weeks I will post this as a new topic with the question I want to discuss as title. greetings, Jens
  15. First of all: sorry I am really late in answering (was too much occupied by the other thread). I will answer all your comments. No.I agree with you: I think those cycles could really have played a role in producing more homogenous molecules as source for life. And initial life could have replaced the steps one by one. But the metabolism first theory really assumes that those cycles become more and more complex by themselve and become life at a certain point in time. This is what I (and not only me, it is the default view) argue against. (The metabolism first try to show that life is inevitable.) This is not part of this topic. Not because I am afraid talking about it, but it is really a separate topic (you are free to open up a new topic). I am looking forward to discuss them with you. {I have written:...has already brought up by de Duve and Miller [43]: Any environment which allows for spontaneous polymerization near chemical equilibrium will simply randomize any sequence information (and kill life). RNA molecules with randomized sequence cannot be the start of life and further evolution.} I fully agree with what you have written.However, the argument from de Duve (and I agree) was a purely thermodynamical one. Wächtershäuser claimed that conditions on the surface (via binding the polymer to charged mineral surfaces) could change in a way that polymerization could happen spontaneously near chemical equilibrium (remember that the metabolism first theory assumes life is autotrophic right from the beginning). So ultimately the chemical cycles really produce RNA (and not the RNA was produced by something else and is using the metabolic cycles). However polymerizing and hydrolyzing near chemical equilibrium will destroy any specific sequence of RNA nucleotides. Please read my full text (as mentioned above): http://www.jfreund.de/dateien/early_life_short.pdf I have put quite a bit literature research in it (see all the references) and it is not more speculation than what others publish in those scientific papers. The speculation part I have separated in another topic. (in the same forum, currently rated as "hot" ). To avoid any misunderstandings: I have a scientific education, worked as scientist and I do not have any believes. Especially I do not think any power has created life on Earth. And this topic is not to discuss such things. I really mean this as a scientific disussion. So any hint why you think it is not even worth discussing is appreciated and I will answer (However, you should read it first.) This is a misunderstanding. I will clarify (I have send you a message). This topic is really meant seriously and is based on more than 50 scientific articles (see references in the link in the original post).
  16. Actually, humans do very well support a much lower concentration of O2, lower pressure and higher pressure, absence of N2 and arbitrary concentrations of H2O. Yes, I have seen avatar and I like the film very much (especially the plant life). However, it is not a scientific source of information . At the temperature range of liquid water, the possible molecules in the atmosphere is not endless, since molecules need to be small. Just assuming a planet with big oceans of liquid water, means that many other possible gases are washed out by rain to a large extend and will be used by microbial life as energy source. Microbes on earth have used and are still using basically any molecule as source of energy which is present in the environment (see for example "Brock - Biology of Microorganisms"). Like on Earth they will all be consumed (CO, SO2, ...). Or those molecules are inert (like N2), but this also means they are not toxic. So actually the molecule that will pose the biggest issue is CO2. This is because of human blood pressure regulation. Even though it does not kill humans immediately you loose consciousness immediately. So for humans (unless genetically "improved" ) a planet is only suitable once it has reached the steady state we have on Earth today: A very low concentration of CO2, because every surplus CO2 has already been consumed by autotrophic life (like plants and cyanobacteria). So from my point of view a planet with liquid water and life will have an atmosphere like Earth over time. Or which toxic molecule in the atmosphere you are thinking about? What you state is very well explained in read "Rare Earth" (Ward D, Brownlee D (2000) Rare Earth. Why Complex Life is Uncommon in the Universe. ISBN 0-387-98701-0, Copernikus, Springer Press, New York.). I have read it. But I am not convinced. As a biochemist looking at the exact details of life, I challenge the assumption of this book that abiogenesis is easy and the evolution from a first cell to a human (or any intelligent life form) is difficult (and I find this a bit human centric). Especially if we can explain the latter (evolution) but not yet the first (abiogenesis). From the biochemistry of life it is only a small step from a microorganism to a human but a big from chemical substances to the first microorganism. The space here is too short to list all the details that we (humans) share with all the existing life forms. However, of course I might be wrong. But more to the facts: The book is completely underestimating the flexibility of life: Temperature range: The only reason why there is no complex life above a certain temperature on Earth is simply because those habitats which are hot and wet do not exist or are simply too small, and not because complex life cannot survive above 50°C or so. Stability: Let’s keep with the definition of the book that complex life is something like plants and animals. All animals suddenly appeared 800 million years ago, after a much longer time period, where only microorganisms were present. This time of 800 million years is the same time in which probably (still in discussion) Earth had a dramatic climatic shift and was completely frozen (snowball Earth). After 10 million years of a snowball so much CO2 accumulated in the atmosphere (because there was no rain any more) that the green-house effect over the equator was just enough to melt the ice there. This then resulted in a dramatic positive feedback (since free water absorbs the light and the heat) that Earth jumped from completely frozen to completely hot within 100 years. This means after those hundred years you suddenly had nice temperatures for life, and an enormous amount of cyanobacteria (still high CO2) which serve as food for those Eukaryotes eating them. This means in such a paradise every cell was surviving, even if it contained a mutation that was not optimal. Surviving the accumulation of mutations that are each a disadvantage and only finally (with the last mutation) form an advantage, is critical to make big steps in evolution. Summary, if the environment is too stable, evolution quickly gets trapped in local optimums. So killing big amounts of life and so that life afterwards can colonize empty habitats with absence of stiff competition is what speeds up big evolutionary progress. And: Rapid climatic changes in east Africa is supposed to have triggered the emergence of homo sapiens. So more climate changes than we had on Earth actually means also quicker evolution. So there are good reasons to doubt that a giant moon is really needed. Changing rotation axis will not stop evolution, quite the opposite is true. Do you have more details on the frequency or magnitude of those changes if there would be no moon?
  17. I do not think so. This is because I view it from the biology point of view and not from the technology point of view. For the chemistry of abiogenesis a liquid phase is needed. And not an arbitrary one. You mandatory need a liquid phase in which complex molecules can form nearly arbitrary but defined (so not random for a given molecule) 3D-structures to act as catalyst for chemical reactions or have any function (actually this means life from a biochemical point of view). In water this is done by the different behaviour of hydrophilic and hydrophobic molecules. RNA, DNA and of course proteins as well as lipid membranes form a hydrophobic center. At the same time most of the other parts of the molecules form specific hydrophilic interactions. More detailed: Actually the hydrophilic interactions are hydrogen bonds and the force which bring hydrophobic parts of the molecules together is mainly the lack of being able to form hydrogen bonds. So flexible but defined 3D structures of macromolecules is linked to liquid phase and hydrogen bonds. This means: liquid water. (the only alternative is liquid NH3). So extraterrestrial life is also bound to liquid water. (I have no idea how likely a planet with liquid NH3 is. I thought that Earth has more oxygen atoms than nitrogen atoms is not just pure chance, but has some systematic reasons. So for the following discussion I will assume that planets with liquid water are much more likely than planets with liquid NH3. I have to do some literature research on this topic.) Keep in mind that hydrogen bounds can only be made by atoms of the 2nd period which are electrophil enough: So only N, O, F. F is too rare to be considered. So H2O and NH3 are really the only possibilities. What would humans do, if we found a planet with liquid water like Earth 800 million years ago? Of course we cannot eat any microorganisms of the extraterrestrial life, since it will definitely have another set of RNA bases and another set of amino acids, if it has amino acids or RNA bases at all. However, since the only way for life to become completely independent of volcanic activity and colonize the oceans is to use water as electron donor for reduction reactions, it is fair to assume that there is a high probability that at some point in time extra-terrestrial life will also evolve photosynthesis and produce oxygen (that is what remains, if you use water as electron donor). So what would we do? We would make an inventory of all the extra-terrestrial life forms and start bringing our own plants to this planet (maybe in closed spaces) and have a nice living there. If it is on average warmer than Earth, we will colonize at the poles where it is colder. If it is on average colder than Earth, we will colonize in the warmest regions. However, since liquid water is a prerequisite for life anyhow, the temperature cannot be so different from Earth. Only if the temperatures are everywhere let's say above 50°C, it will definitely not a nice living, so we might only have a research station there. We would behave the same, if we find a planet which is like Earth 30 million years ago. The only difference is, that we already find bigger organisms which are autotrophic (plants) and others which behave more like parasites (animals). What is if we find something like Earth now? This means with an intelligent life form which is about to destroy big parts of biological diversity on this planet. Either we are egoistic and simply throw this intelligent (but under developed ) life form out and keep a few examples in an open air zoo (just for curiosity). Or we are very concerned about them killing their environment and we start communicating with them. It is unlikely that we simply watch and do nothing. To my point of view your assumption is only working, if you assume that all the earlier intelligent extraterrestrial life forms have found ways to construct artificial habitats in space stations which are much nicer than actually living on a planet surface and do not give a damn about under-developed intelligent species (like us) and their planets (Earth).
  18. (So I think there will be no life found on Jupiter's moon Europa even though it contains liquid water (under several hundred meters of ice).) That is a misunderstanding, too. Jupiter's moon Europa will certainly not contain O2 (and I had not written this). But Europa has a lot of liquid water (and maybe some chemical activity). If we find any life form on Europa my thesis is definitely wrong. If we find nothing that will not proove much, however, it will fit into the picture I have sketched. I have mentioned Europa and the topic above (the O2 in the atmosphere) because that are (to my understanding) the first occasions to prove that my thesis is wrong.
  19. (So I think we did not met other intelligent life forms (or received radio signals) in our galaxy, simply because they do not exist.) With the radio signals I agree that this might actually be really very difficult to receive them even with hypothetical advanced technology (for the reasons you mention). I assume humans will start to find Earth-like planets (with liquid water) within the next 200 years and will probably send at least space probes (without humans) within the next 300 years, which might arrive at this planet within the next 500 years. If our galaxy is full of life we have to assume that some of them had 100 million of years (and not hundreds of years) in advance to us. If there is at least one of those civilizations which behave like us, they had colonized Earth long before we had even the slightest chance to take over. (So I think once we will find the first Earth-like planet, it will show no signs of life (= no O2 in the atmosphere).) This is a misunderstanding. Of course I know that O2 is no prerequisite for life. As you also know it is the other way round: life created O2. This is what I meant: The presence of bigger quantities of O2 means there is life on such a planet. So detecting O2 in the atmosphere of an Earth-like planet is probably the first way of how we can prove the existence of life in another planet without going there. So as soon as we (let's say in 50-100 years from now) are able to detect O2 in the atmosphere of extraterrestrial planets and we find many of them with water and the right temperature but no oxygen this will be an additional indicator that I am right. If on the other side, we detect O2, I am definitely wrong.
  20. (Sorry for late answer, I was one week on a business trip and needed to recover from jet lag...) I am not implying something special: Take the many millions of years of time during that the oceans of earth formed. I am talking about the time were liquid water formed on earth in bigger quantities but still huge amount of water was in the atmosphere. At that time the surface of earth was still very hot and locally there was an enourmous amount of vulcanic activity as well as a lot of meteorite impacts. This is like a giant chemical cooking laboratory in which energy rich molecules are formed all the time and diluted again. This way you create a huge energy gradient necessary for origin of life basically everywhere on the complete surface of earth. And plenty of different molecules emerging life could use. Especially of course huge amounts of condensated phosphates (which autocondensate, it is just a question of concentration and temperature) which can easily be used as energy source. Even though these are conditions like "hell" for current life they are optimal for abiogenesis. Over time replicating molecules became less and less dependent on other molecules in their environment and finally become autotrophic. The best environment for quick evolution (both in nature and in laboratory) is not a constant environment but repeated cycles of proliferation, killing / cleaning, and again colonize empty habitats. This is exactly what earth was providing in the beginning (and not later when all oceans were already settled down). So I think abiogenesis happened on Earth (see http://www.scienceforums.net/topic/71735-early-life-life-could-only-originate-early-or-not-at-all/) So I think abiogenesis had to happen early or not at all. So I think we cannot deduct from early emergence of life, that abiogenesis is a likely event. So I think we did not met other intelligent life forms (or received radio signals) in our galaxy, simply because they do not exist. So I think once we will find the first Earth-like planet, it will show no signs of life (= no O2 in the athmosphere). So I think there will be no life found on Jupiter's moon Europa even though it contains liquid water (under several hundred meters of ice). However, it is not a believe (like you point out very rightly). And I will change my mind, if somebody has better arguments.
  21. There are some contraints, however: Liquid phase seems to be necessary to allow enough chemical reactions in a volume. Most important you need to have the possiblity to have an near endless amount of possibilities of defined 3D structures, so that specific catalysis is possible. The only system which seem to allow for this is a liquid with hydrogen bonds. Given the relative abondance of atoms this means either liquid H2O or liquid NH3. Huge part of the known biochemistry is based on reactions with carbon making double bounds to O, N, C. (Atoms in the next period like Si, P, S cannot do this). So there are some reasons about life beeing based on carbon molecules in water. Those conditions are given between the time liquid water was present and after the last impact which heated the surface of the whole earth to temparatures higher than lets say 150°C and the time stable oceans have been formed. Since I think only under conditions of permament concentration and dilution cycles abiogenesis can happen.
  22. Unfortunately the video cannot bee viewed in Germany (because of the music). But I will try to get it anyway. I Found the PPT form already: http://www.mediafire.com/?jfijmimctnd The following link seems to work (but there is no speaker -- only music. I assume that is correct) http://www.mediafire.com/?yyd0eywkmhj (Again I am not questioning abiogenesis.) I will comment the PPT: - I agree to everything from slide 1-54 - slide 50: "The pre-biotic environment contained hundreds of types of different nucleotides (not just DNA and RNA)." However, there is currently no reason for having one set of nucleotides and one set of bases in one chemically created polymer. So the "1 to self polymerize" is actually very hard to obtain. Since it should distinguish between the different monomers provided (at least not use those which do not allow for proper base pairing at all). - slide 51: "Recent experiments have shown that some of these are capable of spontaneous polymerization, such as phosphoramidate DNA" But even the authors agree, that we do not expect such high energy molecules in nature in the quantity needed (they react with other stuff before). ... and DNA was not there in the beginning (However, but the lack of one OH group in DNA is needed as otherwise you do not obtain a stable structure). Even Szostack is not claiming that this is the solution. It just shows that sponteneous polymerization is possble in principle (in high concentration and clean solutions ....). - slide 56: "Our fatty acid vesicles are permeable to nucleotide monomers, but not polymers". Yes. However the monomers cannot form polymers (nucleotid mono phosphates). What you need to form polymers are at least nucleotid diphosphates. They have multiple electrical charges and do not pass the proposed fatty acid membranes any more. - slide 57, 58, 59: o.k. - slide 60, 61: "Once the temperature cools spontaneous polymerization can occur. And the cycle repeats" I suppose here that in early earth before stable oceans where present, the cycling of heat and cold was much more common and not only at the (quite) rare hydrothermal vents. But mainly of course because the bombardment and strong volcanic environment was constantly concentrating and diluting chemicals which is a source of enrgy rich moelcules of all kinds (much more than you ever find in hydrothermal vents). - slide 69: "Early genomes were completely random and therefore contained NO information." The main issue here is that without specific autocatalysis (by a specific 3D structure determined by a non-random sequence of bases) there is no way to specifically incorporate the right molecules to obtain a polymer chain at all. And not just random chaos network-like macromolecule, which is a mixture of everything available in the environment -- not even base pairing in any reproducable way. However but the base pairing is the prerequisite that evolution can start. So even though the proposal in this slide deck looks good at a first glance it is not plausible from my point of view. I think it is much more plausible to assume a real autocatalytic polymer in the beginning and the specific incorporation comes with the catalytic activity. Or in a summary: Current energy rich monomers have too many charges to pass even an early fatty acid membrane. Theoretical other monomers and polymers with less charges are so energy rich that they will just produce chaos (and not a polymer chain) if available in a natural environment and not in a clean solution in the laboratory. So I doubt the follwing statements in this video - I doubt that the first polymers are without a specific sequence but doing base pairing (this does not seem to be possible) - Hydrothermal vents do not provide those energy rich monomers today. It is better to assume beginning of life during meteorite bombardment to provide the energy rich molecules And maybe the importance of the membranes is overestimated. Actually in the model proposed they are of no use to help polymer formation at all (quite the contrary). It is just that we are used to think life in form of cells. Life could very well started as an autocatalytic molecule without membrane first. ...and thanks again for the link to the video. (I have the underlying article as reference [5] in my document "lonely life") but I was not aware of the video.
  23. Usually (in all books about this topic) it is assumed that life has emerged after stable oceans have been formed. I claim here: - that life has formed already during meteorite bombardment when no stable oceans where present yet. - that life is not coming from another planet. - that life could only emerge under the repeting dilution concentration conditions during meteorite bombardment. This means life had to emerge early or not at all. - ... and I explain why other explanations are less plausible
  24. In heart surgery of children in case of strong cooling (deep hypothermal) there are two strategies with regards of pH regulation: pH-stat: keeping the measured pH constant alpha-stat: let the measured pH increase with falling temperature (actually doing nothing) (If you search in google scholar with "pH-stat alpha-stat" you will see the corresponding publications) I had a discussion with my daughter about it and we came to the following explanation (see chapter explanation below). Anything wrong with this thoughts? Theory: An pH electrode is measuring the absolute concentration of H3O+ (not the relation of [H3O+] to [OH-]). pH value changes caused by temperature changes are biochemically to a large extend irrelevant, because the concentration of OH- is simultaneously also increased (in case of increase of temperature) or also decreased (in case of decrease of temperature). H3O+ and OH- have opposite effect of all those other molecules which can accept or release H+. This means a decrease in temperature also decreases the concentration of H3O+ and thereby increases the pH value (measured by an electrode), but the concentration relation of other buffering substances is unchanged: For example the relation of [H2PO4- ] to [HPO42- ] remains the same. If we could measure the relation of [H2PO4- ] to [HPO42- ] directly and in a simple way, we had a much more appropriate quantity for the acid-base-relation in living organisms or directly in cells. Practice: Out of this considerations you should expect that it is better to not correct the measured pH value of patients which are strongly cooled for a operation at the heart (called alpha-stat strategy). This is because the pOH is increasing simultaneously and the measured change is misleading. But there have been teams which have corrected the increased pH value. (This correction is achieved by adding CO2 in the air breathed in by the patients [1]. This CO2 is partially transforming into H2CO3 , which is releasing H+.) Clinical studies have shown [1] that heart operations with strongly cooled patients statistically have less complications, if the measured pH value had been corrected (pH-Stat strategy). This seems paradox. Explanation: The moderately increased concentration of CO2 in the blood puts the body into the same position as a diver, which has stopped breathing for a while (or more relevant from biological evolution point of view: a child fallen into water). This is valid also because the cooled state also resembles the diving with regards of the temperature (see the diving reflex). It is just reasonable to assume, that the body – caused by the increase of CO2 concentration – takes all measures intended by the evolution, to avoid damages caused by lack of oxygen. A part of this is especially the increase in peripheral resistance to concentrate the blood flow for the survival critical organs [2]. This explains directly the decrease of complications (especially decrease of brain damage) caused by CO2 supply. pH-Stat strategy therefore is a wrong term. You should better call it CO2-supply strategy. Keeping the misleading measured pH constant is just by chance and has most likely nothing to do with the effect. Consequences: Supplying even more CO2 (and simlutaneaously keeping a high oxygen concentration) could have an even improved effect. It is also possible (but less likely) that a combination of alpha-Stat and CO2-supply gives the best results. However, this means you have to compensate the pH-effect of the CO2-supply by other means (infusion?). (preferably of course to be tested with mamals which also show a weak diving reflex like humans). References: [1] Du Plessis AJ et. al. “Perioperative Effects of Alpha-Stat Versus pH-Stat Strategies for Deep Hypothermic Cardiopulmonary Bypass in Infants”, J Thorac Cardiovasc Surg 1997; 114:991-1001 http://intl-jtcs.ctsnetjournals.org/cgi/content/full/114/6/991 [2] Angell James J, De Burgh Daly M “Cardiovacular Responses in Apnoeic Asphyxia: Role of Arterial Chemoreceptors and the Modification of their effects by a Pulmonary Vagal Inflation Reflex, J. Physiol. (1969), 201, pp. 87-104 http://jp.physoc.org/content/201/1/87.full.pdf (sorry for reference [2] which is very old, but I could not qickly find a newer one which is publicly available for free)
  25. I do not understand your comment "flawed assumption". Do you really think different genes always have been there already? (basically meaning at its extreme that the first living organism already had all the genes of a human). Since you obviously do not mean this, we probably talk aside of each other (most likely because I am talking about a 3000 million year time frame). So I will try to rephrase what I show in Figure 1: - It is a comparison of 10 homologous protein sequences (and not a whole genome). - There are 4 different species (green, black, pink, blue). - There are 3 different proteins functions: A, B, Z (so A, B, Z are paralog to each other) - Z is a protein only present in species blue and green. - The different species are very ancient in branching (so from Archea, Bacteria, Eukarya) - The beginning of the tree shows LUCA (the last universal common ancestor of all life) - In the beginning LUCA only had one protein (protein A) Of course LUCA did not had all the genes already. Some of the genes evolved later. Since today there are still plenty of protein families (families of paralogs) in which the individual genes show clear homology even though they have different functions, you have to assume that those paralogs have been created initially by a copy of the gene. Or what is your proposal how this should happen? I am not sure, if I understand what you mean. Protein B has a different function than protein A. For this reason there are highly conserved regions in protein B which differ from those in protein A. This is the reason why all protein B (in the 4 different species) are more close to each other than to protein A. Maybe we discuss it with Figure 2: I wanted to illustrate, that comparing paralogs means that every tree you obtain also partially (or fully -- depending on the time frame) contains the functional distance tree and systematically shows the branching points of paralogs as too early. This might be trivial for method experts like you, but it is very often not taken into consideration in publications about individual genes or individual gene families (especially since there are many hidden paralogs, because in most cases we do not know the regualtion features of the proteins compared). I have read through this reference first (really interesting!): (As you have already mentioned it is about a complete phylogeny of thousands of DNA sequences and not about a single protein family) It is in line with regards that abviously the moelcular clock is not constant (in conserved regions) but of course also is highly sensitive to changes in function. So also here most likely also partial paralogs of the Ultra Conserved Elements have been compared since the authors suggest that their function has changed during evolution from fish to amphibia. We just do not know the function enough to even decide, if the homolog is a paralog or an ortholog. (This is actually quite a typical case). I think this indicates that the UCE are like rRNA part of multilateral interaction in very large complexes similar to splicosomes, translation initiation complexes or ribosomes. And (like in ribosomes, splicosomes, initiation complex) that every change has a broad effect on multiple proteins. The latter is clear, since the paper suggests that they are switches wich have a broad effect in embryogenesis. Both reasons make many tiny individual mutations deadly and the likelyhood of changes very low. RNA is still important today. If only the DNA sequence is the active part of UCE, it would be less conserved (less complex 3D interactions).
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